In the casting of molten metals such as aluminum apparatus and processes have been developed for the simultaneous casting of a plurality of logs, billets or round ingots, hereinafter logs, so as to increase the efficiency and productivity of the casting processes. In such processes and apparatus, a casting table having a plurality of apertures or molds is mounted over a pit from which emerge an equally numbered plurality of hydraulically operated bottom blocks. Each of the bottom blocks is registered, i.e. aligned with, one of the molds. The casting table includes troughs or distribution channels for the dissemination of molten metal introduced thereto to each of the individual molds or apertures located in the casting table. As metal from the distribution channels or troughs in the casting table enters the individual molds, the plurality of bottom blocks is lowered in unison to allow for removal of metal that has solidified in the mold therefrom and to provide space for the introduction of additional incoming molten metal. Such a prior art casting table is shown in FIG. 1 and described in greater detail hereinafter.
While the metal distribution of the casting tables of the prior art as depicted in FIG. 1 have proven highly useful and reliable over many years of service in a multitude of installations, they suffer a number of shortcomings.
As those skilled in the molten metal casting arts are well aware, it is critically important that molten metal reaching each of the molds or apertures at substantially the same time with minimal temperature loss to obtain a successful cast of the plurality logs being simultaneously cast. If metal reaching one or more apertures is too hot or hold time is too short and does not solidify as the base plate descends, a “bleedout” can result. In such a condition, molten metal can be brought into contact with water applied as a spray in the process to cool the solidifying metal. Such a conditions requires rapid plugging of the aperture or mold that is experiencing the “bleedout” with the result that that portion of the production is lost for the cast. Alternatively, if metal has resided in the mold for too long a period, it may be cooler than the balance of the molten metal and therefore solidify more quickly in the mold than metal entering other molds in the casting table resulting in a “freeze-in”, i.e. the solidified metal becomes caught in the mold. Freeze in can drop out during casting and also result in bleedout. Such a condition can result the aborting of the cast entirely and necessitating a freeing up of the metal caught in the mold and a restart of the cast. Such errors can cause significant productivity losses and place operators in significant danger from a safety standpoint. If metal enters the mold with too much velocity or too hot, penetrates between the mold and the head, solidified ingot head “flashing” may occur. Flashing is another condition that may result in molten metal coming into contact with cooling water applied to the ingot below the solidification point. Flashing also causes damage to molds or distortion or delays in the bottom block movement that can also result in casting defects, bleedouts or complete table freeze in.
In addition to the foregoing, as will be explained in greater detail below, the design of the prior art “dams”, i.e. barriers that control the flow of molten metal into the distribution troughs within the casting table, often required the presence of at least two operators on the casting table at the initiation of a casting drop to “lift” or remove the dams at the start of the cast. The presence of operators in the immediate vicinity of the molten metal casting operation is always a safety concern, and the ability to eliminate the exposure of operators to such a risk is critically important to casting facilities.
Finally, the mold portions of the prior art casting tables comprise multi-part elements that require assembly in the casting table costing valuable assembly or set-up time and which because of their design leave exposed joints between the individual elements of the assembly that are sometimes prone to leaking, particularly if not properly assembled.